On Wed, Apr 22, 2009 at 05:56:21PM +0200, Jan Kara wrote:> These three functions are quite similar so merge them to save superblock list> traversal code. As a bonus we get livelock avoidance for all these superblock> traversals. Also remove the condition that if wait == 0 and sb->s_dirt is> not set, then ->sync_fs() is not called. This does not really make much sence> since s_dirt is generally used by filesystem to mean that ->write_super() needs> to be called. But ->sync_fs() does different things. I even suspect that some> filesystems (btrfs?) sets s_dirt just to fool this logic.

Some more comments after looking at it in more details:

- the FSSYNC_SUPER case really needs to do a trylock on the mutex, otherwise any in-progress sync would block pdflush for a long time. And as any real sync should write out the superblock it's not needed anyway during that time. (Need to double-check the filesystems, though) - sync_filesystems really should move to fs/sync.c - I get more and more inclined to make sync just case of looping over the superblocks and do an fsync_super. A plain sync fsync_super might be too slow so we can try to do an async one first and then a sync one as a second pass - that wakeup_pdflush in do_sync looks extremly fishy, we need to do all page writeback via sync_inodes_(sb) anyway, and doing this in parallel from pdflush just introduced tons of potential race opportunities - now if sync_filesystems just ends up calling __fsync_super for the normal sync path I wonder if there really is a point unifying it with the periodic write_super case.